Shanxian Chemical
SUPPLEMENTS
Standardization of NaOH with Potassium Hydrogen Phthalate
Calibration of sodium hydroxide with potassium hydrogen phthalate
1. Objective of the experiment
To master the method of calibrating the concentration of sodium hydroxide solution with potassium hydrogen phthalate as the reference substance.
2. Experimental principle
Potassium hydrogen phthalate ($KHC_ {8} H_ {4} O_ {4} $), its molecule contains a hydrogen atom that can be replaced by a base, and the stoichiometric ratio of reaction with sodium hydroxide is 1 dollar: 1 $. The reaction is as follows:
$KHC_ {8} H_ {4} O_ {4} + NaOH = KNaC_ {8} H_ {4} O_ {4} + H_ {2} O $
When the stoichiometric point is reached, the solution is alkaline, and the pH $is about 9.1 dollars $. Phenolphthalein can be used as an indicator. According to the mass of potassium hydrogen phthalate and the volume of the sodium hydroxide solution consumed, the exact concentration of the sodium hydroxide solution can be calculated.
III. Experimental Instruments and Reagents
1. ** Instrument **: analytical balance, electronic balance, alkaline burette, 250 mL conical flask, 25 mL pipette, volumetric flask (100 mL, 250 mL), beaker, glass rod, rubber head dropper.
2. ** Reagents **: sodium hydroxide solid, potassium hydrogen phthalate (reference material, dried to constant weight at 105 dollars - 110 ^ {\ circ} C $), phenolphthalein indicator (0.2 dollars\% $ethanol solution).
IV. Experimental steps
1. ** Preparation of Sodium Hydroxide Solution **
Weigh an appropriate amount of sodium hydroxide solids in a beaker, add an appropriate amount of freshly boiled and cooled distilled water, stir to dissolve, transfer to a reagent bottle, dilute with distilled water to a certain volume, shake well, label for later use.
2. ** Preparation of Potassium Hydrophthalate Standard Solution **
Accurately weigh a certain quality (calculated according to the required concentration and volume, generally weigh 0.4 dollars - 0.6 g $) Dried to a constant weight of potassium hydrogen phthalate reference material in a small beaker, add an appropriate amount of distilled water to dissolve, quantitatively transfer to a 100 dollars mL $volumetric bottle, dilute with distilled water to scale, shake well.
3. ** Calibration of Sodium Hydroxide Solution **
Pipette 25 dollars mL of potassium hydrogen phthalate standard solution into 250 dollars mL $conical flask, add 2 dollars - 3 $drops of phenolphthalein indicator, titrate with the sodium hydroxide solution to be calibrated until the solution changes from colorless to reddish and does not fade within half a minute, which is the end point. Parallel titration of 3 dollars $times, record the volume of sodium hydroxide solution consumed each time.
V. Data recording and processing
1. ** DATA RECORD **
| Number of Titrations | Potassium Hydrophthalate Mass/g | Consumption $NaOH $Solution Volume/$V_ {1}/mL $| Burette Initial Reading/$V_ {0}/mL $| Actual Consumption $NaOH $Solution Volume/$V = V_ {1} - V_ {0}/mL $|
| :---: | :---: | :---: | :---: | :---: |
| 1 | | | | |
| 2 | | | | |
| 3 | | | | |
2. ** Data processing **
According to the reaction formula, $n (KHC_ {8} H_ {4} O_ {4}) = n (NaOH) $, $c (NaOH) =\ frac {m (KHC_ {8} H_ {4} O_ {4})/M (KHC_ {8} H_ {4} O_ {4}) } {V (NaOH) } $ ($M (KHC_ {8} H_ {4} O_ {4}) $is the molar mass of potassium phthalate).
Calculate the concentration of sodium hydroxide solution for each calibration $c_ {1} $, $c_ {2} $, $c_ {3} $, then find the average $\ overline {c} $, and calculate the relative mean deviation.
Relative mean deviation $=\ frac {\ sum_ {i = 1} ^ {3}\ vert c_ {i} -\ overline {c}\ vert} {3\ overline {c}}\ times100\% $
6. Precautions
1. Sodium hydroxide solids are easy to deliquescent and easily absorb carbon dioxide in the air, so weigh quickly.
2. When dissolving the sodium hydroxide solid, it should be stirred while adding water, and then transferred to the reagent bottle after heat dissipation.
3. The judgment of the titration end point should be accurate. The reddish color will not fade within half a minute. If the red color is too deep, it will lead to high titration results.
4. When titrating in parallel, the solution in the burette should be packed near the zero scale every time to reduce the error.
1. Objective of the experiment
To master the method of calibrating the concentration of sodium hydroxide solution with potassium hydrogen phthalate as the reference substance.
2. Experimental principle
Potassium hydrogen phthalate ($KHC_ {8} H_ {4} O_ {4} $), its molecule contains a hydrogen atom that can be replaced by a base, and the stoichiometric ratio of reaction with sodium hydroxide is 1 dollar: 1 $. The reaction is as follows:
$KHC_ {8} H_ {4} O_ {4} + NaOH = KNaC_ {8} H_ {4} O_ {4} + H_ {2} O $
When the stoichiometric point is reached, the solution is alkaline, and the pH $is about 9.1 dollars $. Phenolphthalein can be used as an indicator. According to the mass of potassium hydrogen phthalate and the volume of the sodium hydroxide solution consumed, the exact concentration of the sodium hydroxide solution can be calculated.
III. Experimental Instruments and Reagents
1. ** Instrument **: analytical balance, electronic balance, alkaline burette, 250 mL conical flask, 25 mL pipette, volumetric flask (100 mL, 250 mL), beaker, glass rod, rubber head dropper.
2. ** Reagents **: sodium hydroxide solid, potassium hydrogen phthalate (reference material, dried to constant weight at 105 dollars - 110 ^ {\ circ} C $), phenolphthalein indicator (0.2 dollars\% $ethanol solution).
IV. Experimental steps
1. ** Preparation of Sodium Hydroxide Solution **
Weigh an appropriate amount of sodium hydroxide solids in a beaker, add an appropriate amount of freshly boiled and cooled distilled water, stir to dissolve, transfer to a reagent bottle, dilute with distilled water to a certain volume, shake well, label for later use.
2. ** Preparation of Potassium Hydrophthalate Standard Solution **
Accurately weigh a certain quality (calculated according to the required concentration and volume, generally weigh 0.4 dollars - 0.6 g $) Dried to a constant weight of potassium hydrogen phthalate reference material in a small beaker, add an appropriate amount of distilled water to dissolve, quantitatively transfer to a 100 dollars mL $volumetric bottle, dilute with distilled water to scale, shake well.
3. ** Calibration of Sodium Hydroxide Solution **
Pipette 25 dollars mL of potassium hydrogen phthalate standard solution into 250 dollars mL $conical flask, add 2 dollars - 3 $drops of phenolphthalein indicator, titrate with the sodium hydroxide solution to be calibrated until the solution changes from colorless to reddish and does not fade within half a minute, which is the end point. Parallel titration of 3 dollars $times, record the volume of sodium hydroxide solution consumed each time.
V. Data recording and processing
1. ** DATA RECORD **
| Number of Titrations | Potassium Hydrophthalate Mass/g | Consumption $NaOH $Solution Volume/$V_ {1}/mL $| Burette Initial Reading/$V_ {0}/mL $| Actual Consumption $NaOH $Solution Volume/$V = V_ {1} - V_ {0}/mL $|
| :---: | :---: | :---: | :---: | :---: |
| 1 | | | | |
| 2 | | | | |
| 3 | | | | |
2. ** Data processing **
According to the reaction formula, $n (KHC_ {8} H_ {4} O_ {4}) = n (NaOH) $, $c (NaOH) =\ frac {m (KHC_ {8} H_ {4} O_ {4})/M (KHC_ {8} H_ {4} O_ {4}) } {V (NaOH) } $ ($M (KHC_ {8} H_ {4} O_ {4}) $is the molar mass of potassium phthalate).
Calculate the concentration of sodium hydroxide solution for each calibration $c_ {1} $, $c_ {2} $, $c_ {3} $, then find the average $\ overline {c} $, and calculate the relative mean deviation.
Relative mean deviation $=\ frac {\ sum_ {i = 1} ^ {3}\ vert c_ {i} -\ overline {c}\ vert} {3\ overline {c}}\ times100\% $
6. Precautions
1. Sodium hydroxide solids are easy to deliquescent and easily absorb carbon dioxide in the air, so weigh quickly.
2. When dissolving the sodium hydroxide solid, it should be stirred while adding water, and then transferred to the reagent bottle after heat dissipation.
3. The judgment of the titration end point should be accurate. The reddish color will not fade within half a minute. If the red color is too deep, it will lead to high titration results.
4. When titrating in parallel, the solution in the burette should be packed near the zero scale every time to reduce the error.
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